1. Field of the Invention
This invention relates to a process for producing acetic acid, and more particularly it relates to a process for producing acetic acid by oxidizing ethylene.
1. Description of the Prior Art
Acetic acid is used as raw materials for producing vinyl acetate, acetylcellulose, acetic acid esters, chloroacetic acid, L-lysine, L-glutamic acid, etc. and has occupied an important position as basic chemicals in petrochemical industry.
As conventional processes for producing acetic acid, methanol carbonylation process, lower hydrocarbon (such as n-butene, 1-butene, etc.) oxidization process, and further acetaldehyde oxidization have been practically employed.
Methanol carbonylation process is a new process wherein acetic acid is produced by reacting carbon monoxide with methanol. According to this process, the reaction has been carried out in the presence of a rhodium carbonyl complex as catalyst in liquid phase under conditions of 180.degree. C. and 28 atm to produce acetic acid with a yield of 99 % based on methanol and that of 90 % based on carbon monoxide. However, since rhodium used as catalyst is extremely expensive, it is necessary to make the catalyst loss as small as possible, and further it has been regarded that the economy of the process is dependent on the cost of methanol as raw material (K. Weissermel and H. J. Arpe, Industrial Organic Chemistry, translated by T. Mukaiyama, page 1, 69, Tokyo Kagaku Dohjin (1978)).
According to the process of directly oxidizing lower hydrocarbons, acetic acid is produced at a single stage. However, since the reaction is carried out under relatively high temperatures and pressures of e.g. 150.degree.-200.degree. C. and 20.about.40 atm, the amount of by-products is so large that a technical problem of improving the reaction selectivity and the yield has been raised. Further, if excess dissolved oxygen is released into the gas phase, hydrocarbons mix with oxygen to have a possibility of troubles such as explosion; hence a countermeasure thereto is required.
On the other hand, according to the acetaldehyde oxidation process, ethylene is oxidized using a catalyst system of palladium chloride (Pd(2)Cl.sub.2)-cupric chloride (Cu(2)Cl.sub.2) under conditions of 100.degree. C. and 10 Kg/cm.sup.2 to first produce acetaldehyde, which is further oxidized using a transition metal ion such as ion of Co, Mn, etc. as catalyst to produce acetic acid. In these reactions, Pd(2) ion capable of oxidizing ethylene cannot oxidize the resulting acetaldehyde and hence the catalysts used at the two stages are different to make direct production of acetic acid difficult.
The object of the present invention is to provide a process having overcome these problems and capable of directly producing acetic acid by oxygen-oxidizing ethylene under milder conditions.